The present invention relates to a hematocrit sensor and a method for measuring hematocrit concentration which, indicates the blood concentration in a blood circuit of a blood purifier that circulates and purifies the blood of a patient.
In dialysis treatments, a blood circuit consisting mainly of flexible tubing is used to place the blood of a patient in extracorporeal blood circulation. This blood circuit arrangement includes an arterial blood circuit having an arterial needle at one end to collect the blood from the patient and a venous blood circuit having a venous needle at one end to return the blood to the patient. A dialyzer can be incorporated between the arterial blood circuit and the venous blood circuit.
A roller blood pump is placed in the arterial blood circuit. By driving the pump, the blood of the patient is collected through the arterial needle and flows extracorporeally through the arterial blood circuit, the dialyzer, and the venous blood circuit. There are multiple hollow fibers inside the dialyzer. The blood flows through each hollow fiber.
Two projections are formed on the dialyzer case, one being a dialyzing fluid inlet port and the other being a dialyzing fluid outlet port. A dialysis device is connected to the two ports. The dialysis device supplies dialyzing fluid of predetermined concentration in through the dialyzing fluid inlet port, along the outside of the hollow fibers (i.e., between the outside surface of the hollow fibers and the inside surface of the dialyzer case), and then out through the dialyzing fluid outlet port.
The walls of hollow fibers, which contain micropores, form blood purifying membranes. Waste products of the blood passing through the inside of the hollow fibers are dialyzed to the dialyzing fluid through the blood purifying membrane and the purified blood returns to the patient. To remove water from the blood of the patient during the dialysis treatment, the dialysis monitor can include an ultrafiltration pump.
The amount of water to be removed (water removal rate) is regulated by controlling the driving speed of the ultrafiltration pump. However, if too much water is removed or if water is removed too quickly, the volume of the circulating blood of the patient is excessively reduced such that blood pressure drop or shock may be induced. On the other hand, if the water removal rate is too low, the treatment duration may be prolonged and the burden to the patient can be too great.
Therefore, as disclosed in Japanese laid open patent publication number Hei 11-221275 and Japanese laid open patent publication number 2001-540, there are blood treatment devices that control the rate of water removal while monitoring the condition of the patient. These existing blood treatment devices have used hematocrit values and other blood parameters to monitor the condition of a patient's blood. The hematocrit value is an indicator of blood concentration, and is expressed as the ratio of red blood cell volume to whole blood volume.
In general, although the hematocrit value during water removal may be in the range of 10 to 60%, the actual value during water removal would be higher than the normal value if the patient experiences shock or blood pressure drop as a result of excess water removal volume or excess water removal rate. By monitoring hematocrit values in real time during water removal that occurs as part of dialysis treatment, the real time measured values could be used as a basis for controlling the driving of the ultrafiltration pump. Based on this parameter, an appropriate water removal rate could be set, which exerts the least burden on the patient. A means for monitoring hematocrit values and controlling the ultrafiltration pump can comprise a blood circuit (for example, a flexible tube) that is arranged between a light emission means and a light reception means. The light emission means and light reception means face each other. The light emission means emits irradiated light, which is received by the light reception means. Accordingly, the rate of light transmitted through the blood in the blood circuit can be measured, and the hematocrit value can be obtained based on this measurement.